1. Field of the Invention
The present invention relates to a ferrule for connecting optical fibers used in optical communication, and to an optical fiber connector using the same. Further, the present invention relates to a method for fabricating such a ferrule for connecting optical fibers.
2. Prior Art
In many optical communication systems, optical fiber connectors have widely been used in portions in the optical lines required to connect between the optical fiber lines or to switch between optical devices and transmit/receive ports, and to adjust or measure optical devices. Usually, such optical connection for coupling optical fibers is achieved by connecting a pair of ferrules fixing optical fibers, both ends of the optical fibers being in contact with each other at the ends of the ferrules.
An Example of conventional ferrules used in the optical fiber connectors is described in Japanese Patent Publication JP 2000-193847, as shown in FIG. 6, wherein an insert 10, having a fine central hole, which is made of ceramics or glass, is buried and fixed in the recess in an end portion of an cylindrically elongated, hollow ferrule body 2, which is made of metal, such as stainless steel, brass or albata. In fabricating, the insert have been inserted into the end surface of the holder by pressing, fitting or bonding, thereby assembling a ferrule.
Also, another type of ferrule has been known, as shown in FIG. 7, in which, similarly, an longer insert 10 of ceramics is inserted into an ferrule body 2 at a flange portion, by pressing, fitting or bonding with an adhesive. The ferrule body is made of metal, e.g., stainless steel, in a substantially cylindrical shape.
Such a ferrule is connected to an optical fiber whose end is inserted through the through hole of the holder into the opening surface of the insert.
In connecting a pair of ferrules, the ferrules are inserted through a sleeve fixed inside a connector body on opposite sides to abut the end surfaces of both ferrules, then connecting the end surfaces of the fibers to be capable of passing a beam of laser light from one optical fiber to the other.
Fabrication of the conventional ferrules shown in FIG. 6 and 7 has required some steps of press fitting or bonding the insert into a opening of the holder, and therefore, previously machining of the joining portions of the holder has been carried out with high accuracy to achieve required dimensions in the joining portions. It has also been necessary to machine a conical or tapered opening 220 extending in the end of the fine hole 11 in the insert 2 in order to easily introduce the end portion of the optical fiber along the through hole 21 of the holder 2 into the fine hole 11.
After assembling the ferrule body 2 and the insert 10, further, the holder has been subjected to precise grinding in the defined outer diameter by taking reference to a center axis of the fine hole 11, because the periphery of the ferrule body must be highly concentric with the fine hole 11 of the insert 10. However, there has been a problem that the concentricity around the holders so fabricated often are deviated, although within the standard range. Further, this mechanical grinding operation is an important factor to increase production cost of ferrules, and ferrules must have lower price.
While prior art ferrules are made by machining the insert 10 on the fine hole 11 and the peripheral surface thereof with a high accuracy in advance and then joining the ferrule body 2 thereto as described above, the desired degree of concentricity between the fine hole 11 and the peripheral surface of the ferrule body 2 could not be achieved, and then, additional machining of the periphery has been required to improve the concentricity.
An object of the present invention is to provide a method of producing an ferrule comprising an insert having hole to fix an optical fiber and an ferrule body to fit the insert on an end thereof which has a high dimensional accuracy in peripheral diameter of the ferrule body.
Another object of the invention is to provide a method of producing such an ferrule with high dimensional accuracy, particularly, without machining the ferrule.
In the present invention, an ferrule is provided which comprises: an ferrule body of a cylindrical shape through which a through hole extends concentrically; and an insert on the end of the ferrule body formed with a fine hole communicating to the through hole in the ferrule body in order to fix an end portion of an optical fiber passing through the through hole of the holder into the fine hole of the insert, wherein the ferrule body is formed of synthetic resin and has concentricity of 10 xcexcm or less of the peripheral surface with respect to the center of the fine hole of the insert.
In the present invention, to fix the end portion of a fine optical fiber, the fine hole is set to be finer than the through hole, and therefore a tapered face is provided between the fine hole in the insert and a through hole in the ferrule body. The tapered face may be formed at the end of the insert or, more preferably, on the side of the ferrule body.
In the present invention, an ferrule is fabricated by the steps of: fixing an insert in an end portion of a cavity formed with a profile of a ferrule body to be molded in a mold, the center of the fine hole being positioned and supported on the center of the cavity by a tapered tip of a cylindrical core arranged along the center of the cavity; and injecting a synthetic resin into the cavity to produce the ferrule body in the end of which the insert is imbedded.
In the method of injection molding, the insert is integrated with the ferrule body made of the synthetic resin after injected and cured in the cavity, and then the periphery of the ferrule body may be prepared with high dimensional accuracy with reference to the center of the insert hole, then, achieving high concentricity of the ferrule body to the fine hole of the insert to eliminate the need for machining the peripheral surface of the holder.